Hydraulic fluid composition



tion of corrosion.

Patented Jan. 29, 1952 HYDRAULIC FLUID COMPOSITION Aaron Wachter andNathan Stillman,'Berkeley,

Calif., assignors to Shell Development Company, San Francisco, Calif., acorporation of Delaware No Drawing. Application 'June 8, 1946, :SerialNo. 675,445

1 Claims. (01. 252-77) ,The present invention relates tocorrosion-inhibiting compositions and particularly tocorrosion-inhibiting hydraulic fluid compositions which become dilutedwith water during their normal life-time. More particularly theinvention relates to fluid compositions useful in by draulicallyoperated apparatus, to pressure- .transmitting fluid compositions, andto heat exchange fluid compositions, said fluid compositions containingsubstantial amounts of water, water-soluble organic materials, and anovel and useful class of corrosion-inhibitors. More specifically, thisinvention relates to aqueous hydraulic fluids and/or aqueous heatexchange media which contain certain corrosion-inhibiting compounds orsubstances, which when present in the liquid phase of these media, notonly inhibit corrosion of metals contacting the liquid, but also inhibitcorrosion of metals during the time that they are exposed to the vaporphase above such a liquid aqueous media.

In the past it has been known to add various substances to hydraulicpressure fluids or heat exchange media in order to inhibit or partiallyprevent corrosion of metals contacting these 'liquid media. However,none of the additives which were used as corrosion-inhibitors weresunicient- 1y satisfactory because of one .or more of a number ofreasons, among which were: only partial corrosion-inhibition which onlysomewhat delayed break-down or repairs of the hydraulic mechanisms used;insuiiicient solubility or compatibility bf the additive with thehydraulic fluid; the difficulty that previous corrosion inhibitors whichare soluble ,in organic substances are not sufiiciently soluble oroperative when the organic substances are diluted with water; economicunavailability; and other disadvantages. In general, previouscorrosion-inhibitors had the serious disadvantages of being whollyineffective in the vapor phase above the liquid in the system, and ofbeing only partially effective in the liquid phase in many cases.

It is an object of the present invention to overcome the above and otherdefects. A primary object of this invention is to provide novelcompositions of matter comprising water-containing organic media andsuitable additives, which compositions provide liquid-vapor phaseprevenpresent invention to provide a method of inhibiting corrosion ofmetals in both the liquid and vapor phases attendant uponwater-containing hydraulic fluid ,or heat-exchange systems. It is stillanother object to provide com ositions use- It is another object of thei f u1 in such a method, which compositions comprise a minor amount ofone or more additives contained in initially anhydrous polarwater-soluble organic liquid media which are normally subject todissolving or dispersing water therein during their use. A furtherobject is to provide a class of substaces suitable in water-containingliquid media for inhibiting corrosion of metals in both the liquid and.vapor phases.

As described in :the patent application Serial No. 557,358, filedOctober 5, 1944, now abandoned, of which the present application is acontinuation-in-part, it has been recently discovered that corrosioninhibition of ametal, which is normally corrodible by contact with watervapor, or liquid water, and/or air, may be realized -by providing theatmosphere surrounding such metal with the vapors of certain organiccorrosion-inhibiting compounds or substances known herein as vapor phasecorrosion-inhibitors. These inhibitors may be organic base .nitrites,compounds having a nitro-aliphatic nucleus, compounds having anitro-phenol nucleus, and/or various other organic compounds. It hasfurther been. discovered that a preferred class of such inhibitorsconsists of or comprises organic base nitrite salts, especially organicnitrogeneous base nitrite salts. In general, the organic base nitritesalt which is to be employed as the inhibitor should preferably have avapor pressure of at least 0.00002 mm. of Hg at 21 0., and preferablygreater than about 0.0001 mm of'I-Ig at 21 C.

It has now been discovered that the above and other objects, involvingessentially corrosion-inhibition in either or both the liquid and vaporphases, are attained by acomposition comprising or containing salts ofan organic base with nitrous acid dispersed in a water-containingorganic medium. More specifically, in accordance with the invention,these corrosion-inhibiting salts are disposed in a water-containinghydraulic fluid or heat exchange liquid, and the thuspreparedcomposition is then used as a hydraulic or heat exchange liquid. It hasbeen further found that usually the most preferred inhibitors fordispersion in the media for the purposes mentioned, are the secondaryamine nitrites. Also, the media wherein the present inhibitors are usedshould have a pH value of at least about '6, preferably about 57, whilehigher pH values may be used without detriment. Preferably, the presentvolatile organic nitrite salts should'have a watersolubility pf about 1%by weight, or higher, although the degree of water-solubility may bevery low. Also, the inhibitor employed in the present type of mediashould have a vapor pressure of at least 0.00002 mm. of Hg at 21 C., andpreferably greater than about 0.0001 mm. of Hg at 21 C. The presentclass of inhibitors which prevent corrosion of metals in both the liquidand vapor phases, may also be termed liquid-vapor phasecorrosion-inhibitors. It has also been found that the metal walls orparts enclosed within hydraulic machines are prevented from corroding byemploying therein'a hydraulic fluid containing one or more organic basenitrite salts; this hydraulic fluid may initially be anhydrous.

Representative classes of organic bases which are suitable for preparingthe salts used as vapor phase inhibitors according to the presentinvention, include: primary amines, secondary amines, tertiary amines,cyclic secondary amines of the type of piperidine, oxazines, morpholine,

thiazolines, and pyrrolidine; and various nitrogenous bases such asurea, thiourea, hydrazines, hydroxylamines, amidines, and guanidine. Inany of the above nuclei, alkyl, cycloalkyl, terpinyl, bornyl, aralkyl,benzyl, phenyl, aryl, and various substituent groups or atomic radicalsmay be present so long as the sum total basicity of the nitrogenouscompound is approximately equal to or greater than the acidity ofnitrous acid with which it forms a salt. Among the substituent groupsthe alkyl and cycloalkyl groups are preferred. I

The basicity of the various basic constituents of the class of saltsdescribed herein is described, for example, in The Organic Chemistry ofNitrogen by N. V. Sidgwick, 1937 edition, and in Organic Chemistry byPaul Karrer, 1938 edition.

More specifically and preferably, organic nitrogen base salts of nitrousacid include the following nitrite salts of 1. Primary amines, such as(a) primary amines in which the amine group is attached to a secondaryor a tertiary aliphatic carbon atom as in the following structuralforwherein R1, R2 and R are hydrocarbon radicals which are aliphatic,alicyclic, heterocyclic, aromatic, ar alkylated cyclic radicals, andmay, if desired, contain preferably not more than one olefinic doublebond, or R1 and R2 are joined in the form of a cyclo-aliphatic orheterocyclicaliphatic ring radical Rs;

(b) primary amines in which the amine group is attached to an aralkylgroup as in the following structural formula:

wherein R4 is an aromatic hydrocarbon radical, preferably a phenyl oralkylated phenyl radical and n is an integer which is preferably 1 or 2;

(0) primary aliphatic amines, such as methyl amine, which react withnitrous acid in the presence of an excess of the amine to give a primaryamine nitrite salt, (as distinguished from a primary aliphatic aminewhich reacts with nitrous acid to yield nitrogen, an alcohol, or otherreaction products).

2. Secondary amines, such as secondary amines in which the amine groupis attached to an aliphatic carbon atom, preferably a secondary ortertiary carbon atom, as represented by the 1301- lowing structuralformulas:

wherein R1 and R2 are hydrocarbon radicals as in l (a) and wherein R1and R2 may be joined in the form of a ring forming R3 NH which is eitherN-alicyclic or contains in the R3 portion of the organic ring atoms ofthe type of oxygen and/or sulfur.

3. Tertiary amines.

4. Quaternary ammonium bases pyridinium bases.

Specific examples of organic nitrogen bases suitable for preparation ofthe organic nitrogen base nitrite salt vapor phase corrosion inhibitorsof the present invention include:

Primary amines: methylamine, isopropyl amine, Z-annino-butane, tertiarybutyl amine, 2-amino-4-methylpentane, various amyl, hexyl, heptyl,octyl, and higher homologous primary amines wherein the group isattached to a secondary or tertiary carbon atom; cyclopentyl amine,alkylated cyclopentyl amines, cyclohexylamine, mono-methylcyclohexylamines, dimethyl cyclohexylamines, trimethyl cyclohexylamines,other alkylated cyclohexylamines, bornyl amine, fenchyl amine,cycloterpenyl amines, pinyl amine, benzylamine, beta-phenylethy1 amine,alkylated benzylamines, tetrahydro betanaphthylamine, allyl amine,beta-methyl allyl amine, beta-chloro allyl amine, and their homologs andanalogs.

Secondary amines: di-methyl-, di-ethyl-, din-propyl-di-isopropyl-,di-butyl-amines; various secondary amines derived from amyl, hexyl,heptyl, octyl, and higher homologous alkyl groups; methyl isobutylamine, N-methyl N-tertiarybutyl amine, N-alkyl N-cyclohexyl amine,N-alkyl N-bornyl amine, di-bornyl amine, N-methyl N cycloterpenyl amine,N-isopropyl N-(l)-methyl amine, N -alkyl N-benzyl amines and theirhomologs and analogs; dicyclopentyl amine, dicyclohexyl amine, alkylateddicyclohexyl amines; diphenylamine, dibenzylamine, di-(beta phenylethyl) amine; piperidine, piperazine, alkylated piperidines orpiperazines; 1,4-alkylated and unalkylated oxazines such as morpholineand 2,4,4,6-tetramet-hyl tetrahydro-1,3-oxazine;alkylated-1,3-thiazolines such as 2,4,4,6-tetramethyltetrahydro-3-thiazoline.

Secondary amine type derivatives of alkylene diamines, such as:

wherein R1 and R3 may be like or different aliphatic, alicyclic,aralkyl, alkarylalkyl, heterocyclic, terpenic radicals, and wherein R2is an alkylene or cycloalkylene radical. These R1 and R3 radicals forinstance, may be isopropyl, butyl, cyclohexyl, benzyl, and/or bornylradicals. The R2 radical is preferably an ethylene or propylene radical.

Tertiary amines: trimethyl amine, triethylamine, tri-n-propylamine,tri-isopropylamine, tributylamine, higher homologous and isomerictrialkylamines, variously N-substituted tertiary amines having differentorganic radicals on the amino nitrogen atom, e. g., alkyl, alicyclic,bornyl, fenchyl, aralkyl, and like homologs and analogs;

including and tertiary amine type derivatives of alkylene diamines.

Organic nitrogenous bases, particularly guanidine; also diazoles,imidazolines, e. g., 2+heptyl- Z-imidazoline, diazinespyr imidines,'and'the like.

Quaternary ammonium bases: 'te'tramethyl, tetraethyl, and highertetraalkyl ammonium bases; trimethyl benzyle, tr-imethyl eyclohexyl-,tributyl decy'l ammonium bases; various quaternary N-su'bstitutedammonium'bases having various organic radicals (of-the type describedabove) on the quaternary'nitrogen atom; 'pyridinium and alkylatedpyridinium or ouinolin'ium quaternary ammonium bases having an alkyl,cycloalkyl, or aralkyl-group on the quaternary nitrogen atom, includingmethyl butyl, cyclohexyl, benzyl :groups and like 'homologs -or analogs.

The various hydrocarbon radicals or groups of the above organic basesmayalsocontainstable and inert polar substituent atoms or radicals, suchas, chlorine, ether, thio-ether, alcohol, free aminoyor-nitro groups.'Neutral'ketone, ester and ,nitrile groups and aliphatic unsaturationmay also be present, particularly in the case of allyl and chlorallylgroups.

The salts of nitrous acid and the organic nitrogen bases-describedabove, may be prepared by a stoiohiometric reaction of an organic :nitrogen base with nitrous acid while maintaining the reaction mixture atleast slightly basic incharacter.

Other organic salts of nitrous acid which are suitable vapor phaseinhibitors according to the present invention are the sulfonium,phosphonium, or iodonium organic nitrate salts. Among these oniumnit-rites, the sulfonium nitrites are preferred. In general,nitritesalts of the isologs of the ammonium compounds, commonly termedonium compounds, and which have the general formula 'RXHy wherein R isan organic radical which may be alkyl, cycloalkyl, aryl, alkaryl, orheterocyclic; X is an element selected from the group consisting ofphosphorus, arsenic, antimony, carbon, oxygen, sulfur, selenium, tin andiodine; and v1 is an integer which varies from 2 to 4 depending on thevalence of X, may suitably be appliedas vapor phase inhibitors.

Generally, where the pH value of the present hydraulic liquidcompositions is normally greater than about 6, the presence of a basicagent is not necessary. Where the hydraulic liquid has a pHperse of lessthan about 6 or a potential pl-I when contacted with waterof less thanabout 6, then the stability of the liquid-vapor phase inhibitors,particularly of the organic nitrogenbase-nitrite salts,,is adverselyafiected. 'The'stability of the inhibitors is usually also adverselyaifected by elevated temperatures, particular y those of about 12091, to150 .or higher. The efiect of such .and like factors which render anorganic nitrite unstable, is greatly lessened or even entirely obviatedby associating with the inhibitor, or the media in which it is disposed,a basic-acting substance. Where a preliminary trial test with a specifichydraulic fluid indicates the need of a basic agent, the latter isusually dispersed or dissolved in the hydraulic fluid prior to theintroduction therein of the organic nitrite inhibitor. Suitablestabilizing agents include basic agents which are organic or inorganiccompounds that provide apI-I value'in excessof'about 7 when dispersed inwater. Suitable stabilizing agents also include basic materials havingbasic dissociation constants greater, approximately temperatures.

equal to, or slightly less than the dissociation constant of the organicbasic material which combined .to form thenitrite salt which it may bedesired to stabilize. In many cases .a preferred stabilizing agent isthe free .organic nitrogenous base which corresponds to that which wasused in the preparation of the organic nitrogenousbase nitrite salt.

As wasstated, the present invention is applicable to the prevention ofcorrosion of metal parts incontact with either a water-containing vaporphase, or a liquid phase .or both. Prevention of such corrosion is moreparticularly applicable in the cases of machinery, instruments, and thelike which are subject to corrosion during their normal operation as .aresult of moisture condensation or the presence of a moist atmosphere,as for example in the case of .gyroscopic flight stabilizers, bomb sightmechanisms, hydraulic mechanisms, turbine gears, or like situationspresent in other mechanisms. "Prevention of the corrosion .of'thesurfaces of metal in contact with the vapor spaces present and enclosedby such mechanisms is obtained by including a corrosionpreventingquantity of one or more of the inhibitors according to the presentinvention, thus maintaining the desired inhibiting atmosphere in contactwith the metal surfaces normally tending to become corroded. Forexample, in hydraulic gun recoil mechanisms, it has-been'found that theatmosphere in the air space above the hydraulic fluid contained in themechanism will corrode adjacent metal surfaces, but by the addition of avolatile organic base nitrite salt inhibitor to the hydraulic fluid,such corrosion is entirely obviated. At the same time the inhibitors ofthe present invention are generally sufficiently soluble in both waterand either watersoluble organic materials or hydrocarbon materials,other water-insoluble organic liquids, and the like, that the corrosivetendencies present on the metal contacting the liquid phase are alsoentirely obviated.

The presently described inhibitors are more effective in preventingcorrosion of metal parts occurring in the presence of water at a pHvalue of approximately 7, or 8, or up to a pH of 12 or even higher andmore particularly prevent such corrosion of ferrous metals, e. g.,steels, and also aluminum, nickel, chromium, and alloys of these'metals.

As an alternative to the incorporation of an organic nitrogenous-basenitrite salt into a hydraulic fluid, more particularly wherecorrosioninhibiting action immediately followin addition of the fluid tothe mechanism is not desired or needed, the nitrosamines which maybeformed from a secondary or primary amine nitrite ,salt maybeincorporated into a hydraulic fluid with The relationship between cerandthe nitrosamines consists .of an equilibrium which may be stated asfollows:

wherein at least one R, and preferablyboth R's, represent an organicradical, and one of the *Rs may be the hydrogen atom. The aboveequilibrium with the nitrosamine and'water which may be formed from theamine ,nitrite or vice verse, undergoes a shift toward increasingconcentrations of the nitrosamine at increasingly higher According tothe usual laws of equilibrium, an excess of either water or nitrosamineabove "the chemical *mol ratios present in dispersed in water.

' in Water.

any given equilibrium results in increasing the concentration of theamine nitrite. More specifically, it has now been found that watersolutions of nitrosamine slowly yielded increasing concentrations of theamino nitrites and that such solutions when employed as a hydraulicfluid, prevented corrosion of contacting metal parts under conditions ofa pH value of at least about 6.

The present inhibitors may advantageously be incorporated in anysubstantially neutral or basic organic substance which is liquid,semi-solid, or substantially solid, in which the inhibitor is soluble,or with which the inhibitor may bestably Preferred organic materials arewater-soluble organic materials, or those which are capable of formingstable dispersions By a water-soluble organic substance is meant a polarorganic solvent material which contains a sufiicient number ofwater-solubilizing groups that it is at least partially miscible withwater. Water-soluble organic materials include: low molecular weightmono-hydroxy alcohols,

low molecular weight ketones, lowmolecular weight amines, polyhydroxyalcohols, certain water-soluble amides and amines, low molecular weightesters, various hydroxy-esters, hydroxyethers, hydroxy-nitriles,polyamino compounds, and neutral quaternary ammonium compounds.Representative specific examples of the various types of compoundsbelonging to the broad class of water-soluble organic compounds include:methyl alcohol, ethyl alcohol, propyl alcohol, glycerol, ethyleneglycol, diethylene glycol, glycerin mono alpha chlorohydrin, propyleneglycol, triethylene glycol, sorbitol, mannitol, pentaerythritol,diacetone alcohol, acetone, methyl ethyl ketone, dioxane, etc. Of thesethe more preferred are the less volatile alcohols such as the glycols,other higher molecular weight polyhydric alcohols, and the like. Othersuitable water-soluble organic materials include: butyl amine, propylamine, ethylene diamine, 1,3,5- triamino pentane, alkanol amines, e. g.,mono, di-, and triethanol amines, polyether polyamino compounds,morpholine, acetamide, formamide, urea, ureides, ethyl acetate, ethyllactate, polypropylenoxypolyhydric alcohols, polyethyleneoxy aliphaticpolyethers, diethylene glycol monoalkyl ethers of e. g. methyl, ethyl,propyl, and butyl alcohol, diethyl ether of diethylene glycol, 1,2-dihydroxy-acetonitrile, 2 hydroxy-acetonitrile, glycol monoricinoleate,betaine, the various water-soluble betaine derivatives, and likecompounds. Other types of compounds which may be used to make up watersolutions with the present inhibitors include: trialkyl phosphates, e.g., triethyl phosphate, dipropyl potassium phosphate, disodiumphosphate, salts of organic carboxylic, sulfonic, and sulfate acids,sodium naphthenates, soaps, e. g., combinations of acids from castoroil, soybean oil, and various other oils, particularly of ricinoleicacid with alkali metal hydroxides, also trimethyl benzyl ammoniumchloride, trimethyl lauryl ammonium hydroxide, or carbohydrates such asmannose, glucose, and various other suitable water-soluble compounds.Some of the less preferred but still suitable organic media used as anessential constituent in hydraulic fluids include: such alicyclic,aromatic, and amino alcohols as cyclohexanol, fenchyl alcohol, borneol,terpenic alcohols, benzyl alcohol, tetrahydrofurfuryl alcohol,ethoxyaminobutanol, and the like; ethers such as diisobutyl ether, ethyltertiary butyl ether, methyl ricinoleyl ether; aldehydes such ashept- 1. aldehyde, capryaldehyde; ketones such as diisopropyl ketone,cyclohexanone; nitrogen-containing compounds such as octyl amine,ethylene diamine, etc. Y

The present corrosion-inhibitors may be added by incorporating one ormore of them into any one or more of the water-soluble organic materialsdescribed herein, either with or without water. In many cases it isadvantageous to incorporate the inhibitor into the substantiallyanhydrous water-soluble organic material and then dilute such acomposition, later with water prior to use as a hydraulicpressure-transmitting medium.

Although the proportion or relative concentration of the organic basenitrite which is to be added to a water-soluble organic material to in-'hibit or obviate corrosion of a metal in contact therewith in thepresence of water, may vary within wide limits, it is usually preferredto add the smallest eiiective amount. This is usually between about 0.01wt. per centand about 30 wt. per cent of the total compositionwhendiluted with Water, although for most average cases'it is desirable toemploy between about 0.1 wt. per cent and about 5W1}. per cent of thetotal composition. With the corrosion-producing conditions usuallyencountered with a glycol-water base hydraulic fluid, approximately0.01% to 5% by weight of the total hydraulic composition is usuallysufficient.

While the present organic base nitrites are referred to as being addedto a water-soluble organic substance, which contains or is to containwater, it is to be understood that in some instances suchcorrosion-inhibitors may also exist in the present type of compositionswhen they are obtained, for example, during the preparation of theorganic base nitrite in isopropyl alcohol-water mixtures, or in ethyleneglycol-water mixtures. In such case, as long as a corrosioninhibitingamount of the organic base nitrite is present in the organo-aqueoussolution, it may be used directly, or with suitable modification (as bythe addition of other additives) employed as an energy-transmittingfluid.

Generally, the compositions described herein may also contain any of theadditives known to be compatible with water. For example, the salts ofstrong inorganic or organic acids and alkyl polyamines and/or of alkylolamines which are known to have no tendency to vaporize and at the sametime to markedly depress the freezing point of water, may be added. Forinstance, triethanolamine salts of such acids as phosphates, oleates,palmitates, and stearates or the like may be disposed .in the liquidmedia containing the described corrosion-inhibitors. Onium bases mayalso be used, either in a solution or in an emulsion, particularly ofthe oil-in- Water type. The onium base is an aid in inhibiting corrosionof the metals but only in the liquid phase; the onium base alsostabilizes the emulsion by neutralizing any traces of acid which mayoccur. The presence of inorganic salts, such as sodium chloride, calciumchloride, magnesium sulfate, etc., in the aqueous system, does notseriously reduce the eifectiveness of the present organic base nitritesalts as corrosion inhibitors.

Other aqueous media, more particularly anti freeze compositions, towhich the present invention is applicable, are water solutions of urea,guanidine, and the like, e. g., preferably 25 wt. percent to 33 wt.percent of urea in Water, or of aureid of glucose and urea in water. Inplace of urea many other amides may be. used, prefe erably 30 wt.percent of either acetamide or formamide, or both, in water with a fewper cent of the present salts of nitrous acid and an organic base. Otherantifreeze compositions, comprising a water solution of a Water-solublesubstance having a betaine nucleus, more particularly of trimethylbetaine, as in a 50 wt. percent solution, or more or less, areadvantageously treated with the present vapor phase inhibitors, thuspreventing corrosion when used.

The present vapor phase corrosion-inhibitors are advantageouslyincorporated in non-aqueous pressure-transmitting fluid compositionswhich have a tolerance or capacity for dissolving water therein, usuallyup to about 20 wt. percent of Water or even higher. Examples of thistype out non-aqueous compositions include: conventional hydraulic brakefluids made up of various percentages of neutralized or. slightlyalkalized castor oil, ethylene glycol, Carbitols, with or withoutethanol or other alcohol; more generally, typical pressure fluidcompositions which comprise essentially any one or more of the followingtypes of compounds, viz., glycerine, a glycol, a. glycol ether, a loweraliphatic alcohol, and an ethanolamine; a major amount of di-ethyleneglycol monoethyl ether (.Carbitol) with a minor amount of fusel alcohol;a major amount of fusel. alcohol with a minor amount of triethanolamine;a minor amount of triethanolamine lactate with a major amount ofCarbitol; a minor amount of triethanolamine ricinoleate witha majoramount of isopropyl alcohol (or butanol) a minor amount of propyleneglycol ricinoleate and a major amount of isobutanol; and organic solventdiluent with a ricinoleyl alcohol, a ricinoleyl ester, or a ricinoleylamine, e. g., about 50 wt. percent isobutanol, about 16 wt. percentmethyl ricinoleate, and the rest a mixture of common polyhydricalcohols; mixtures of ricinoleyl alcohol and tetrahydrofuriuryl alcohol,e. g., in approximately equal parts by weight; a mixture ofcyclohexanone-glycerine and tetrahydrofuriuryl alcohol; etc. Suchhydraulic fluid compositions normally absorb water into solution becauseof unavoidable contact with water during their use. In any casehydraulic fluid compositions of the water-tolerant type are greatlyimproved by' having dispersed therein an organic base nitrite salt,preferably one or more of the volatile nitrite salts formed by theaddition of nitrous acid to an organic nitrogenous base. Inthis waynormally corrodible metals contacting such fluids both in the vapor andliquid phases are prevented from corroding asa result of the waterintroduced into these fluids during their use.

The present vapor phase inhibitors also have outstanding merit whenemployed as the corrosion inhibitor in resin-containing hydraulicpressure fluids. For example, a suitable composition having substantiallubricating value due to its viscosity properties has as its predominantconstituent an artificial. resin formed from aromatic sulfonamidescondensed with formaldehyde. About 10 wt. per cent of this resin isdissolved in about 15 wt. per cent of a plasticizing ester ofpentaerythritol and/or dipentaerythritol and aliphatic or organic fattycarboxylic acids. Along with the resin and plasticizer there is usedabout 5 wt. per cent of. a chemical polishing agent capable ofchemically attacking the microscopic projections of a metal surface andsmoothing them out as relatively soft compounds. The total wt. per centof the resin, the plasticizer. and the. polishing agent is usually aboutwt. per cent: and the remainder of, the composition. (of to about 68 wt.per cent or somewhat. higher), is preferably made up with. a. solvent ofthe type of a monoethyl ether of diethylene glycol. Preferredliquid-vapor phase inhibitors: in this; composition, according to thepresent invention, are about 0.1 wtper cent to 2.0 wt. per cent,orhigher', of di-isopropyl amine nitrite, or di-cyclohexylamine nitrite.This hydraulic composition mixes readily with the more importanthydraulic brake. fluids commonly used. in. industry, if such. an.admixture. is desired. The specified. resin. and. plasticizercontaininghydraulic fluid. has a water tolerance of approximately 19 wt. percentat. ordinary room temperatures (about 75 F-.)., Other. suit:- ableinitially non-aqueous hydraulic fluids. may be composed of castor oiladmixed with. ethanoh A good hydraulic fluid working at. low coldtemperatures may be; made. up of. anyone or" more ofv the following:ethylene glycol, ethylene. glycol monoethyl ether, diethylene glycolmonoethyl; ether, vfusel oil, isoamyl, alcohol, diacetone alcohol, orthe like thoroughly admixed. in. each case; with. triethanol. amine andcontaining preferably 0.1: wt. per cent to 5.0 wt. per cent ofv one orthe present organic base nitrites as the essential.

corrosionsinhibitor. These: produce especially practicable hydraulicfluids. Thus; a mixture of 50 wt. per cent triethanolamine and. 49 wt.per cent diethylene glycol monoethyl. ether COIL-r taming 1 wt. per centor di-cyclohexyl ammonium nitrite does not boil until about 389 F., doesnot adversely affect rubber in the. system, and has a. satisfactorilyuniform viscosity. A mixture 01 about 49 wt. per cent ofv triethanol.amine, and about 50 wt. per cent of. diacetone. alcohol. GOD? taining.about 1 wt. per cent of guanidine nitrite. or di-isopropyl'. ammoniumnitrite or morphelinium nitrite is one of a number of. compositionswhich is especially suitable for thepurposesmentioned.

The present. organic vapor phase corrosioninhibitors may also beincorporated with. pres-- sure-transmitting liquids. of the type whichare substantially insoluble in water. Some examples. of this. typeofliquid include hydrocarbons. such as hexanes, heptanes, octanes,benzene, toluene, xylenes, cyclohexane, naphthas, kerosene,.alkylates,gas; oils, light lube oils, trimethyl-cyclo hexane, naphthenes, mixturesof diphenyl. oxide, aniline, and naphthalene, mixtures of 13013161310.rinated. benzenes' and polychloroalkylated henzenes, mixtures of a.mineral oil with a poly.- merized; hydrocarbon, hydrogenated ornon-hydrogenated synthetic polypropylenes, polyalkylene oxides,.polyalkylene-esters, estersv such as.2;-ethyl; hexyl sebacate, variousother water-insoluble. or.- ganic compounds, etc. media, thepolyalkyleneoxides (.e. g.,. polypropyl-- eneor polyethylene oxides),although substantially not miscible withwater for most purposes, willdissolve up to: aboutB wt. per cent of water. The other substantiallywater-insoluble. organic: liquids tolerate evenv less water butordinarily do absorb water as av trace in solution, or asv asuspension.

The present organic vapor phase corrosion-irrhibitors are also highlyuseful when incorporated with a hydraulic fluid comprising or consistingof sulfolane or alpha-sulfalene, or: substituted compounds having thesuli'olane or alpha-subfolene nucleus, e. g., ZA-dimethylsulfolane.allyl'. 3-sulfol'anol ether, 3-methylsu1'folane, 3-sulfolanyl.

Oi. the mentioned liquid.

11 amine, tetrahydrofurfuryl 3-sulfolanyl ether, etc. Often thesulfolane's or alpha-sulfolenes along with the present inhibitors areadmixed with various organic solvents such as alcohols, esters, etc.,and/or with various lubricants. Usually from about 5% to about 95% byvolume of a sulfolane relative to the finished hydraulic fluid isemployed.

Additional materials may also be included in the hydraulic fluid ifdesired. For example, it will at times be found advantageous to add asmall proportion of graphite either alone or in fluid suspensions, suchas those known under the trade names of Castordag, Aquadag, Glydag, andthe like which are suspensions of graphite in castor oil, aqueous media,and a polyalcohol, respectively. Quantities ranging from about 0.001 toabout 0.5% by Volume of graphite based on the total fluid compositionare usually satisfactory.

Relevant to the application of the present invention to heat exchangemedia, the universal heat exchange medium in major use, despite manyefforts to produce suitable substitutes therefor, is water. Water ismost used for heat exchange purposes, not because it is ideal, butbecause it is relatively eflicient during the range of temperatures mostcommonly used, is lowest in cost, generally readily available, and itsboiling point is such that it gives warning of excessive or dangeroustemperatures. Nevertheless when used alone or with various additivespreviously known, water possesses many serious disadvantages. Attemperatures in the neighborhood of 160 F. water begins to vaporizematerially, and such vaporization causes the formation of gaspockets, 1. e., vapor phase regions in which additives to the water usedheretofore are not functional. Furthermore, vapor phase regionscomprising water vapor and the air normally present in such systems arealways present above the liquid phase in such aqueous heattransfersystems. The water, both in the vapor and liquid phases, ishighly corrosive to metals coming in contact therewith, especially thewalls of cooling and heating systems. There then results both rapiddeterioration of such walls and progressively decreasing efficiency ofheat transfer due to the insulating layers of corroded and depositedmaterials.

For low temperature operations in heat exchange media or hydraulicfluids, because of the freezing point of water, its use alone isdecidedly unsatisfactory. Water-alcohol, water-glycerol, water-ethyleneglycol mixtures are commonly used to avoid freezing and reduce thepartial pressure of water vapor above such and the like aqueous media.Many other water-soluble organic compounds having a fairly satisfactorycombination of the sought-for properties are also used for the mentionedpurposes, e. g., n-butyl Carbitol, cellusolve, various ketones, andalcoholic hydroxyl-containing compounds. However, mixtures of water withethyl alcohol, or glycerine, or ethylene'glycol, or with any of thewatersoluble organic compounds indicated herein, are practically ascorrosive to metals as water alone. The introduction of one or moreorganic base nitrites, preferably the organic nitrogenous-base nitritesalts, into any such water-containing mixturesinhibits the corrosion ofthe metal parts attendant upon the use of the heat exchange media.

' The present inventon is thus applicable to the cooling radiators ofautomobiles subjected to forcedcirculation through the radiator, andsome air is 'readilvdissolved in the water. This invention is alsoapplicable to other aqueous sys tems such as hot water and steam heatingsystems, as well as in substantially the same previously describedfundamental manner in hydraulic fluids, also in cutting oil emulsions,also in aqueous grinding fluids containing water-soluble organiccompounds in this instance without a water-insoluble emulsified oilphase. In the use of aqueous cutting oil emulsions, or solutions, thepresence of the present vapor phase inhibitors therein preventscorrosion of the drainage surfaces of the metals in the course of theirbeing subjected to cutting, machining, or grinding.

In all instances the action of the present corrosion-inhibitors appearsto be the same. Being soluble in both water and water-soluble organicmaterials, the inhibitors may easily be incorporated in these organicmaterials before they are diluted with water for, or during thehydraulic purposes at hand. Thus, when the organic material to which theinhibitors have been added is incorporated with water, either bydeliberate introduction of water with agitation in bulk to theconcentration conventionally or otherwise desired for a hydraulic fluid,or by external introduction of water vapor and/or liquid water duringhydraulic operation of the initially anhydrous water-soluble organicmaterial or composition, the water takes up the inhibitor from theorganic material and is rendered innocuous (free of corrosive activity)with regard to the contacting metal surfaces. An important point is thatthe presence of the water-soluble organic material, even in the highestpossible concentra tions in the water does not decrease the solubilityof the present inhibitors below that of a corrosion-inhibiting amount inthe total composition. The present inhibitors are distributedsufliciently in solution in both the organic mol- 40 ecules and thewater molecules that corrosion is efiectively suppressed regardless ofthe relative concentration of the water, be it predominant in amount orapproaching only a few tenths of one per cent.

Generally, as stated above, the present fluid compositions are highlypractical for use in hydraulic machinery for the transmission ofpressures, such as the various hydraulic systems used in the operationof airplanes, in hydraulic brake systems, hydraulic shock absorbers,hydraulic jacks, lifts, presses, recoil chambers, dash pots, et cetera.

For purposes of illustration, reference will be had to the followingspecific examples, it being understood that there is no intention ofbeing limited to the specific conditions disclosed. The percentagesspecified in these examples are percentages by weight unless otherwisespecified.

Example I A freshly cleaned piece of steel plate was immersed for abouthalf its length in a hydraulic fluid made up of 50 parts by volume ofethylene glycol and 50 parts by volume of water, and containing 2 partsby weight of dicyclohexylamine Both tests were carried out in sub-.

assume":

13 amount of corrosion. After thus testin for 7 5'- hours, it was foundthat the steel plate subjected to the control test was heavily corrodedwith orange and brown rust. On the other hand, the steel plate testedwith the hydraulic fluid containing the specified organic base nitritesalts was completely free from any rust or other manner of corrosionafter the 75 hour period of operation.

Example II solubilities of dicyclohexylammonium niitrite in; water.methyl alcohol, and in mixtures of Water and ethylene glycol, which aresuitable as hydraulic fluids, are shown in the following table:

Parts by weigl1tof; Dieyelohexylamrnonium Temperature 7 Q i M 1Mixtutre'fo'f- 5t0 Wt. 1pgr l etuy cen We er am 0 Water alcohol wt:percent of ethyl- 'ene glycol In methanol-water and ethylene glycolmixtures with water, the solubility of dicyclohexylammonium nitritevaries with the solvent composition as follows:

Grams of Dicyelohexylammo'nium Nitrite per 100 grams of SaturatedSolution at 25 C. l'I1'" Wt. Per Cent Water insolvent Mixture Methanolwater Ethylene-Glycol- Mixture Water Mixture Example III The followingis an example of a satisfactory commercial antifreeze composition: 7Pounds Ethylene glycol e 96.5 Water ie -4-.. 2.0

Example IV The following is an example of an improved aqueous alcoholsolution which is useful in the cooling system of a conventionalinternal combustion engine of the liquid-cooled type. To approximately1000 parts by wt. of an alcohol, e. g., methanol, ethanol, ethyleneglycol, or glycerol, 4 to 15 parts by wt. of an oil mixture containingan emulsifier are introduced under vigorous agitation. This oil mixturemay consist of about one and one-half parts of sodium naphthenatesdissolved in about 9 parts of a paraffin base mineral oil having aSaybolt Universal viscosity of approximately 200 seconds at 100 F. Tothe resultant composition there is then added with Nitrite per 100'parts by weight of'Satura-ted 14 vigorous agitation, either with orwithout water; an amount of dicyclohexyl amine nitrite approximatelyequivalent to between about 0.01 wt. per cent and 2 wt. per cent of thetotal composition diluted with water, a 0.5 wt. per cent concentra tionof the amine nitrite being preferable. The

finished composition is then made up by'i'ncorporating any amount ofwater, depending uponthe degree of lowering of the freezing point ofwater desired. i

Example V A hydraulic fluid composition containing a bodying agent hasthe following composition: 70% monohydric alcohol consisting of 55 partsby wt. of butyl alcohol, 10 parts by wt. of mixed amyl alcohols and 5parts by wt. of hexyl and heptyl alcohols, 14 wt. per cent ethyleneglycol monoricinoleate, and about 2 wt. per cent of one or more of thepresent organic base nitrites, e. g., di-cyclohexyl amine nitrite,morpholinium nitrite or preferably di-isopropyl amine nitrite. To partsof this mixture there is added 3 parts of a bodying agent such as a lowsubstituted methyl cellulose, or the like.

Example VI Polished st'eel strips were immersed in water solutionscontaining 0.05 wt. per cent and 0.1 wt; per cent of sodium chloriderespectively and also a 0.0145 molar (0.27 wt. per cent) concentrationof 3,3,5-trimethylcyclbhexyl amine nitrite. The containers which heldthese solutions and the steel strips were allowed to stand open to theatmosphere at room temperature for two months. The amine nitrite inthese solutions completely protected the steel strips from rustingduring t 0 months of operation. In a control test without the aminenitrite a steel strip was badly rusted in less than one hour.

Example VII Drops of the solutions described in the above Example VIwere placed upon steel strips which were then stored in closedcontainers, each of V which had an atmosphere having 100% relativehumidity. The storage period was for ten days at room temperature. Theamine nitrite present in the drops of salt water solutions on the steelcompletely protected the steel from rusting. The results showed that thepresence of the amine nitrite prevented the rusting normally caused bywater drops on steel air.

Example VIII Example IX Specimens of aluminum, copper, brass, and solderinch by 2 inches) were coupled by steel bolts and placed in watercontaining 30 wt. per cent of ethylene gylcol, and also in a likesolution except that it contained an added 4.2 wt. per cent ofmorpholine nitrite. These two solutions were refluxed for hours inall-glass apparatus. In

the ease in which the morpholine nitrite was present, it was found thatthe weight losses for all of the metals were substantially less thanthose obtained in the control test, and no sediment was formed in thesolution. On the other hand, in'the control test without the organicamine nitrite inhibitor, there was a large amount of loose black andrusty sediment formed in th solution. 7

The present application is a continuation-inpart of the copendingapplication Serial No. 557,358, fded October 5, 1944, now abandoned.

We claim as our invention:

1. As a composition of matter, a hydraulic fluid comprising essentiallya predominant amount of a mixture of ethylene glycol and a substantialamount greater than about 2 weight per cent of water, and between about0.01 weight per cent and about 30 Weight per cent of a secondary aminenitrite salt having a vapor pressure of at least about 0.0001 mm. of Hgat 21 C., the amount of 1 said salt being based upon the total weight ofsaid composition, said composition having a pH of at least about 6. Y

2. As a composition of matter, a hydraulic fluid comprising essentiallya predominant amount of a mixture of ethylene glycol and a substantialamount between about 2 weight per cent and about 70 weight per cent ofwater, and between about 0.1 weight per cent and about 5 weight per centof a secondary amine nitrite salt having a vapor pressure of at leastabout 0.0001 mm. Hg at 21 C., the amount of said salt being based uponthe total weight of said composition, said composition having a pH valueof at least about 6.

' 3. As a composition of matter, a hydraulic fluid comprisingessentially a predominant amount of an alcoholic hydroxyl-containingwater-soluble organic compound and a substantial amount greater thanabout 2 weight per cent of water, and between about 0.01 weight per centand about 30 weight per cent of a dicycloalkylamine nitrate salt havinga vapor pressure of at least about 0.0001 mm. Hg at 21 C., the amount ofsaid salt being based upon the total weight of said composition, saidcomposition having a pH of at least about 6.

4. As a composition of matter, a hydraulic fluid comprising essentiallya predominant amount of a mixture of a water-soluble organic compoundand a substantial amount greater than about 2 weight per cent of water,and between about 0.01 weight per cent and about 30 weight per cent of asecondary amine nitrite salt having a vapor pres- 16' sure of at leastabout 0.0001 mm'Hg at 21" C2, the amount of said salt being based uponthe total weight of said composition, said composi tion having a pH ofat least about 6.

5. As a composition of matter, a hydraulic fluid 1 6. As a compositionof matter, a hydraulic 'fluid comprising essentially a predominantamount of a mixture of a water-soluble organic substance and asubstantial amount greater than about 2 weight per cent of water, andbetween about 0.01 weight per cent and about 30 weight per cent of anorganic nitrogen-base nitritesalt having a vapor pressure of at leastabout 0.00002 mm. Hg at 21 0., the amount of said salt being based uponthe total Weight of said composition, said composition having a pH of atleast about 6.

7. As a composition of matter, a hydraulic fluid comprising essentiallya predominant amount of a mixture of a water-soluble organic substanceand a substantial amount greater than about 2 weight per cent of water,and between about 0.01 weight per cent and about 30 weight per cent ofan organic base nitrite salt having a vapor pressure of at least about0.00002 mm. Hg at 21 C., the amount of said salt being based upon thetotal weight of said composition, said composition having a pH of atleast about 6.

AARON WACI-ITER. NATHAN STILLMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. AS A COMPOSITION OF MATTER, A HYDRAULIC FLUID COMPRISING ESSENTIALLYA PREDOMINANT AMOUNT OF A MIXTURE OF ETHYLENE GLYCOL AND A SUBSTANTIALAMOUNT GREATER THAN ABOUT 2 WEIGHT PER CENT OF WATER, AND BETWEEN ABOUT0.01 WEIGHT PER CENT AND ABOUT 30 WEIGHT PER CENT OF A SECONDARY AMINENITRITE SALT HAVING A VAPOR PRESSURE OF AT LEAST ABOUT 0.0001 MM. OF HGAT 21* C., THE AMOUNT OF SAID SALT BEING BASED UPON THE TOTAL WEIGHT OFSAID COMPOSITION, SAID COMPOSITION HAVING A PH OF AT LEAST ABOUT 6.